Amplified wavelength broadband video distribution architectures

ABSTRACT

Provided herein are embodiments of a device, method of use and system for a low-cost analog multi-wavelength video distribution transamplifier for CATV and FTTH networks having a broadband overlay. The transamplifier embodiments described herein allow the use of multiple wavelengths to segment logical service groups in a CATV distribution system and a FTTH system having a broadband overlay.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. application Ser. No. 11/765,152,filed on even date herewith and entitled, “Amplified WavelengthBroadband Video Distribution Architectures Using an ExternalWaveguide,”.

TECHNICAL FIELD

The present disclosure relates generally to optical signal transmissionand more specifically to amplification of optical signals at a pluralityof wavelengths in a video distribution system.

BACKGROUND

In the mid 1990's it became obvious that the world-wide consumerappetite for bandwidth hungry applications would eventually mean a shiftnot only in the consumer electronics that deliver the “experience,” butalso in the way that access networks would be deployed and used. At thetime, while advances in data delivery over legacy copper networks (DSLfor instance) and the implementation of hybrid-coaxial deploymentsseemed to suffice it was clear that in a short time both of thesemethods would have severe shortcomings to available end line customerapplications. By the early years in this decade, the acceleratedavailability of high definition television programming, video-on-demand,VoIP, peer to peer gaming, IM, video uploading, etc, made the need forimproved access immediate.

In 1998, ITU-T released the standard G.983.1, incorporated herein byreference, that was recommended by the Full Service Access Network(FSAN) group with the intent of working towards a truly broadband fiberaccess network. This initiative is generally known as the FTTH BPON,(“B” for broadband, and “PON” for passive optical network). One goal ofthis recommendation was making the delivery of data burdeningapplications, particularly high end video, as inexpensive as possible.At the physical layer, this means fully leveraging the almost unlimitedbandwidth transmission capacity of a fiber waveguide, and for costreasons sharing one central optical line terminal (OLT) over as manyoptical network units (ONU) as possible in a point to multipointdistribution configuration. A typical ratio is 16-64 ONU per OLT.

Implicit in the BPON recommendation is the ability to deliver the voice,data and video (e.g., the “triple play”) with specific designation tomeet these requirements even at the physical layer. The type ofinformation slated for transport in this specification can be brokeninto three types of services: broadcast (general and directed ornarrowband), downstream, and return path services.

In a typical deployment there can be multiple hundreds up to thousandsof PON in operation. Many of these PON are serviced by the same backbonetransport system. “Downstream” is the specific information onlyparticular to one ONU in a PON. Its delivery is managed by the OLT anddependent on the transport and networking specification use. Examples ofdownstream service include telephony, video on demand, and high speeddata via ATM.

“Broadcast” is information that all ONUs of a particular OLT receiveequivalently and exactly. Broadcast includes, for instance, nationallysyndicated TV channels such as NBC, CBS, and ABC, or locally syndicatedchannels such as, for example, city council TV. “General broadcast”occurs when the same information is provided to all ONUs of many OLTs ina deployment (e.g., NBC, ABC, CBS, etc.) A “directed broadcast” occurswhen all ONU's of a considerable subset of OLTs from of a deploymentreceive the same information (e.g., city council TV). Broadcastinformation and narrowcast information can be any form of data, voice orvideo. For example, in one instance broadcast information can be datasuch as QAM to a modem. Likewise, narrowcast information can be datasuch as QAM to a single modem or a subset of modems.

“Return path” is the upstream information that allows a closed loopinformation exchange system.

Generally, in a typical PON architecture there are four optical bands ofoperation, the 1270 nm to the 1350 nm band for the upstream, the coarsewave-division multiplexing (CWDM) band above the water peak up to 1480nm for future upgrades, the 1480 nm to 1500 nm for the downstream, andthe 1550-1560 nm range for downstream broadcast distribution. Thehardware implemented is also particular with function and expectation.At a central office (CO) resides an OLT, which is an ATM basedtransceiver to transmit at 1490 nm and receive a 1310 nm signalgenerated by the ONU module. Also, at the CO is the placement of a 1550nm transmission and the optical amplification necessary to transmit abroadband RF spectrum signal. The combination of the downstream signalsand the drop of the upstream signal at the CO happen through a passivewide band filter. The input/output of this passive multiplexer isincident on one optical fiber and per the ITU specification can have amaximum logical reach of about 20 km for the BPON, with some distancevariation for GPON and EPON configurations. Nearing the end of this PONdistance there is a high count 1×N optical splitter, after which eachfiber terminates at an ONU, typically a residence or business of somesort.

A typical ONU comprises an optical triplexer, which takes the input fromthe 1490 and 1550 nm upstream signals and separates them for independentreception, and takes the upstream 1310 signal and adds it to the PONfiber. Also comprising the ONU are the opto-to-electrical conversionproperties of the receiver diode, amplification, and AGC circuit setsthat prepare the signal for demodulation at the TV or set top box videoreceivers. The purpose of the video overlay (over the optical network(e.g., PON)) is to transmit a portion of the radio frequency spectrum(55 MHz to 1 GHz) to each ONU, a proven technology for high qualitytransmission of analog amplitude modulation and QAM. QAM modulation isQuadrature Amplitude Modulation, a symbol based modulation whereamplitude and phase components exist according to baseband digitalsubsets. The QAM symbol capacity can differ, from 64 to 1024 symbolschemes, but most typically 256 symbol modulation is used. Currentlydeployable transmission capacity for the video overlay is quite large,up to 6.6 Gbps, which can support up to 1256 HD video channels, or 6594SD video channels.

This RF modulation scheme and the leveraging of its transmissioncapacity have been perfected over the last two decades in HFCapplications. HFC architectures have a fiber trunk that terminates at anode followed by a coaxial plant that distributes signal to the enduses. However, it can be advantageous to replace the coaxialdistribution with a PON.

In RF transmission links, both the electronics and optics disrupt theinput signal via various noise sources. The challenge for these types oflinks is that these impairments must all be managed or corrected to acertain extent for efficient interpretation by the end line user. Themain noise sources to contend in these systems are: Relative IntensityNoise (RIN) from transmitter laser and laser to modulator interaction,and from optical amplifiers; intermodulation noise from transmitter,fiber, and fiber scattering; diode and electronic characteristics in theoptical receiver module; and fiber non-linear interaction betweenmultiple wavelengths. The relative intensity noise penalties degrade theRF signal to noise (CNR) parameter per channel over the whole operatingband, the intermodulation noise creates harmonic beating effects (CSOfrom second orders, CTB from third orders) spread statisticallythroughout the operating band, and scattering phenomena appear due tothe high launch powers necessary for cost effective delivery of signal,(SBS (stimulated Brillouin scattering) and SRS (stimulated Ramanscattering) for multiple wavelengths interaction). All of these ifunchecked reduce the necessary quality of service.

As a point of reference, in HFC, for optical fiber terminating at a nodethe specifications per channel are typically carrier to noise ratioCNR>52 dBc, composite second order (CSO)<−65 dBc, and composite triplebeat (CTB)<−65 dBc, while for in FTTH for fiber terminating at an ONUthe specifications per channel are typically CNR>46 dBc, CSO<−53 dBc,CTB<−53 dBc. For QAM transmission at an HFC node the specificationdesired is typically <1E-9 symbol BER (bit error rate), while for a FTTHONU only a <1E-6 symbol BER is required.

With respect to the noise impediments, HFC systems are intermodulationlimited. Thus all the technology development, network design, and costreduction has gone mostly towards creating hardware that can mitigateintermodulation effectively. From the perspective of optical links, thismeans delivering to the coaxial plant very low levels of intermodulationdistortions (e.g. −65 dBc), to be degraded rapidly through RF amplifiersto end delivery at customer site with some margin on typical standard(e.g. ˜53 dBc.) This limit has historically bound the evolution ofoptical networks in HFC. Specifically, this means that without duedesign provisions both at the board and systems level one would expectthe CSO to go out of spec long before the CNR would.

FTTH systems, on the other hand, are more directly limited by factors ofoverall broadband noise sources which come from the interplay ofcomposite laser modulation limits and in particular the shot noisecoming from the optical to electrical conversion in the ONU receivers.These two points describe the maximum CNR per channel for FTTH systems.Practically, it is the case that for both technical reasons and costscalability one wants to design FTTH architectures such that thebroadband 1550 nm portions hits the receiver at the minimum valuepossible. For this case, FTTH systems are often referred to as shotnoise limited. This limit however enables the use of multiple opticalamplifiers in cascade, another distinction to HFC, where operating atoptical input powers into the node higher than 0 dBm the RINcontribution from optical amplifiers can quickly dominate the CNRparameter.

One adverse, but necessary, point of comparison to HFC is that theoptical link budget for PON recommendations is at or above 25 dB. It isknown that while the physical limit of uncorrected sources is 7 dBm intofiber >25 km, which ultimately means that unlike for HFC links, that forFTTH the end of the optics link will be incident at a receiver at powersmuch lower than zero dBm, down to −8 dBm. This then leaves the receivershot noise as the only dominant term to define the CNR for RF channelsin the system, even to the point where other broadband noise terms, suchas RIN from transmitters and amps are far secondary limiting factors.This benefit will become quickly apparent in the discussion of allowableoptical amplifier cascades in FTTH.

Therefore, what is needed is an architecture that overcomes many of thechallenges found in fiber, hybrid-fiber and fiber-deep architectureswith broadband overlays, many of which are described above. Inparticular, what is needed are device, methods and systems to providehigh optical power delivery systems to streamline the implementation andcost of FTTH and fiber-deep architectures while technically maintaininga high quality of service.

OVERVIEW

Provided herein are embodiments of a device, method of use and systemfor a low-cost analog multi-wavelength video distribution transamplifierfor hybrid-fiber and fiber-deep CATV architectures, and FTTH networkshaving a broadband overlay. The transamplifier embodiments describedherein allow the use of multiple wavelengths to segment logical servicegroups in a CATV distribution system and a FTTH system having abroadband overlay.

In one aspect, a transamplifier is provided. The transamplifier iscomprised of one or more optical transmitters. Each optical transmitterreceives an input signal and transmits a transmitter output opticalsignal having a respective transmitted power level. The transamplifieris further comprised of an optical multiplexer having a plurality ofinputs and at least one output. Each of the one or more opticaltransmitters are operatively connected with a respective one of theplurality of inputs of the multiplexer and the output is configured totransmit a combined optical signal comprised of each of the transmitteroutput optical signals having respective transmitted power levels. Thecombined optical signal has a combined power level. Further comprisingthe transamplifier is an optical amplifier having an input and anoutput. The input of the optical amplifier receives the combined opticalsignal, amplifies it and transmits an amplified combined optical signalto the output of the optical amplifier. Further comprising thetransamplifier is an optical demultiplexer. The optical demultiplexerhas an input and a plurality of outputs. The input of the opticaldemultiplexer is configured to receive at least a portion of theamplified combined optical signal, split the amplified combined opticalsignal into a plurality of discrete output optical signals of varyingpower and wavelength sections, and transmit each discrete output opticalsignal to one of the plurality of outputs. In one embodiment, theoptical amplifier can be a multiple-doped fiber amplifier such as acladding pumped amplifier. In this instance, the combined power level ofthe combined optical signal is greater than a threshold power level(P_(min)) at the input of the optical amplifier such that the opticalamplifier is operational and results in an acceptable quality of acommunications channel for each of the discrete output optical signals.In another embodiment, the optical amplifier can be an single-dopedfiber amplifier such as an EDFA amplifier. In other embodiments, theoptical amplifier can be a solid state amplifier. A level of input powerto the optical amplifier is chosen based on operational characteristicsof the optical amplifier chosen and the desired amplification.

In another aspect, a method of tuning a transamplifier is provided. Themethod comprises providing a plurality of input signals to atransamplifier. Desired characteristics for each of a plurality ofoutput discrete optical signals from the transamplifier are determined.Each of said the plurality of output discrete optical signals from thetransamplifier are analyzed. If the analyzed signals do not meet or donot substantially meet the desired characteristics, then thetransamplifier is adjusted to obtain the desired characteristics foreach of the plurality of output discrete optical signals. Adjusting thetransamplifier to obtained the desired characteristics for each of theplurality of output discrete optical signals can include, for example,adjusting one or more of an amplitude of one or more of the plurality ofinput signals to the transamplifier; adjusting the frequency of one ormore of the plurality of input signals to the transamplifier; adjustingthe input power associated with one or more of the plurality of inputsignals to the transamplifier; adjusting output power of one or more ofthe optical transmitters; adjusting power input to the optical amplifierof the transamplifier; adjusting the wavelength of an amplificationsignal provided by the optical amplifier of the transamplifier;adjusting electronic pre-distortion compensation of one or more of theplurality of input signals to the transamplifier, adjusting electronicpre-distortion compensation of one or more electrical signals within thetransamplifier, adjusting optical distortion compensation of one or moreoptical signals within the transamplifier, and by selection of a laserhaving certain characteristics for the optical amplifier of thetransamplifier.

Yet another aspect according to the present invention is a system fortransporting voice, data and video signals over a fiber optic network.The system comprises an optical line termination (OLT) operativelycoupled to the fiber-optic network; an optical network unit (ONU)operatively coupled to the fiber-optic network; a transamplifieroperatively coupled to the fiber-optic network such that the discreteoutput signals of the transamplifier are combined with voice and datasignals from the OLT using WDM and transported to the ONUs through thefiber-optic network.

Additional advantages will be set forth in part in the description whichfollows or may be learned by practice. The advantages will be realizedand attained by means of the elements and combinations particularlypointed out in the appended claims. It is to be understood that both theforegoing general description and the following detailed description areexamples and explanatory only and are not restrictive, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, not drawn to scale, which are incorporated inand constitute a part of this specification, illustrate embodiments andtogether with the description, serve to explain the principles of themethods and systems:

FIGS. 1A-1D are illustrations of a transamplifier in various embodimentsaccording to the present invention;

FIG. 2 is an illustration of a system for transporting video, voice anddata over a fiber optic network in an embodiment according to thepresent invention; and

FIG. 3 is a flowchart illustrating an embodiment of a method tuning atransamplifier according to the present invention.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Before the present methods and systems are disclosed and described, itis to be understood that the methods and systems are not limited tospecific synthetic methods, specific components, or to particularcompositions, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only and is not intended to be limiting.

As used in the specification and the appended claims, the singular forms“a”, “an” and “the” include plural referents unless the context clearlydictates otherwise. Ranges may be expressed herein as from “about” oneparticular value, and/or to “about” another particular value. When sucha range is expressed, another embodiment includes from the oneparticular value and/or to the other particular value. Similarly, whenvalues are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms anotherembodiment. It will be further understood that the endpoints of each ofthe ranges are significant both in relation to the other endpoint, andindependently of the other endpoint.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where said event or circumstance occurs and instances where itdoes not.

The present methods and systems may be understood more readily byreference to the following detailed description of preferred embodimentsand the Examples included therein and to the Figures and their previousand following description.

I. HFC

HFC is a telecommunications industry term for a network whichincorporates both optical fiber along with coaxial cable to create abroadband network. The fiber optic network extends from the cableoperators' master headend, sometimes to regional headends, and out to aneighborhood's hubsite, and finally to a fiber optic node which servesanywhere from 25 to 2000 homes. A master headend or central office willusually have satellite dishes for reception of distant video signals aswell as IP aggregation routers. Some master headends also housetelephony equipment for providing telecommunications services to thecommunity. A regional or area headend will receive the video signal fromthe master headend and add to it the Public, Educational and/orGovernmental (PEG) channels as required by local franchising authoritiesor insert targeted advertising that would appeal to a local area.

II. FTTP/FTTH/FTTC

Fiber to the premises (FTTP) is a form of fiber-optic communicationdelivery in which an optical fiber is run directly onto the customers'premises. This contrasts with other fiber-optic communication deliverystrategies such as fiber to the node (FTTN), fiber to the curb (FTTC),or HFC, all of which depend upon more traditional methods such as copperwires or coaxial cable for “last mile” delivery. FTTN, FTTC and HFC arealso sometimes referred to as fiber deep architectures, meaning thatfiber is run to a node close to the home or premises and coaxial cableor other forms of copper conductors are used to transition the “lastmile” to the home or premises. These architectures are all contemplatedwithin the scope of embodiments according to the present invention.

Fiber to the premises can be further categorized according to where theoptical fiber ends: FTTH (fiber to the home) is a form of fiber opticcommunication delivery in which the optical signal reaches the enduser's living or office space and FTTB (fiber to the building, alsocalled fiber to the basement) is a form of fiber optic communicationdelivery in which the optical signal reaches the premises but stopsshort of the end user's living or office space.

In FTTP, an optical signal is distributed from the central office overan optical distribution network (ODN). At the endpoints of this network,devices called optical network units (ONUs) convert the optical signalinto an electrical signal. The signal usually travels electricallybetween the ONU and the end-users'devices.

Optical distribution networks have several competing technologies. Thesimplest optical distribution network can be called direct fiber. Inthis architecture, each fiber leaving the central office goes to exactlyone customer. More commonly each fiber leaving the central office isactually shared by many customers. It is not until such a fiber getsrelatively close to the customers that it is split into individualcustomer-specific fibers. There are two competing optical distributionnetwork architectures which achieve this split: active optical networks(AONs) and passive optical networks (PONs).

Active optical networks rely on electrically powered equipment todistribute the signal, such as a switch, router, or multiplexer. Eachsignal leaving the central office is directed only to the customer forwhich it is intended. Incoming signals from the customers avoidcolliding at the intersection because the powered equipment thereprovides buffering.

Passive optical networks do not use electrically powered components tosplit the signal. Instead, the signal is distributed using beamsplitters. Each splitter typically splits a single fiber into 16, 32, or64 fibers, depending on the manufacturer, and several splitters can beaggregated in a single cabinet. A beam splitter cannot provide anyswitching or buffering capabilities; the resulting connection is calleda point-to-multipoint link. For such a connection, the optical networkterminations on the customer's end must perform some special functionswhich would not otherwise be required. For example, due to the absenceof switching capabilities, each signal leaving the central office mustbe broadcast to all users served by that splitter (including to thosefor whom the signal is not intended). It is therefore up to the opticalnetwork termination to filter out any signals intended for othercustomers.

In addition, since beam splitters cannot perform buffering, eachindividual optical network termination must be coordinated in amultiplexing scheme to prevent signals leaving the customer fromcolliding at the intersection. Two types of multiplexing are possiblefor achieving this: wavelength-division multiplexing (WDM) andtime-division multiplexing. With wavelength-division multiplexing, eachcustomer transmits their signal using a unique wavelength. Withtime-division multiplexing, the customers “take turns” transmittinginformation.

In comparison with active optical networks, passive optical networkshave significant advantages and disadvantages. They avoid thecomplexities involved in keeping electronic equipment operatingoutdoors. They also allow for analog broadcasts, which can simplify thedelivery of analog television. However, because each signal must bepushed out to everyone served by the splitter (rather than to just asingle switching device), the central office must be equipped withpowerful transmission equipment. In addition, because each customer'soptical network termination must transmit all the way to the centraloffice (rather than to just the nearest switching device), customerscan't be as far from the central office as is possible with activeoptical networks.

A passive optical network (PON) is a point-to-multipoint, fiber to thepremises network architecture in which un-powered optical splitters areused to enable a single optical fiber to serve multiple premises,typically 32. A PON can comprise an Optical Line Terminal (OLT) at theservice provider's central office and a number of Optical Network Units(ONUs) near end users.

Upstream signals are combined using a multiple access protocol,invariably time division multiple access (TDMA). The OLTs “range” theONUs in order to provide time slot assignments for upstreamcommunication.

A PON takes advantage of wavelength division multiplexing (WDM), usingone wavelength for downstream traffic and another for upstream trafficon a single fiber. As with bit rate, the standards describe severaloptical budgets, but the industry has converged on 28 dB of loss budget.This corresponds to about 20 km with a 32-way split.

A PON can comprise an OLT, one or more user nodes (ONUs), and the fibersand splitters between them, called the optical distribution network(ODN). The OLT provides the interface between the PON and the backbonenetwork. The ONU terminates the PON and presents the native serviceinterfaces to the user. These services can comprise voice (plain oldtelephone service (POTS) or voice over IP-VoIP), data (typicallyEthernet or V.35), video, and/or telemetry (TTL, ECL, RS530, etc.). APON is a converged network, in that all of these services are typicallyconverted and encapsulated in a single packet type for transmission overthe PON fiber.

A broadband overlay capacity in PON networks can be thought of in twoways. The most obvious is that it provides a physical layer that allowsdelivery of broadcast video, where most successful operators haveleveraged the cost basis of this layer to deliver general video, whereup to thousands of ONUs receive the same video content for a veryaffordable cost/home. The second capacity is that the BPON provides apipe that can not only serve in general broadcast video distribution,but can also relieve the burden of other downstream video or video likeapplications that burden the OLT with high data rates and stringentthroughput specifications, VOD and switch digital video, for instance.This is generally referred to as directed broadcasting or narrowcast,where the video overlay serving size is not segmented by the thousands,but by the hundreds, even down to 120 ONUs per broadcast signal. Inorder to facilitate such an overlay system comprising broadcast andnarrowcast, embodiments of a transamplifier according to the presentinvention are provided, which can simultaneously segment generalbroadcast and directed broadcast into different wavelengths andamplified sections.

III. TRANSAMPLIFLER

FIG. 1A is an illustration of a transamplifier 100 in an embodimentaccording to the present invention. As shown in FIG. 1, thetransamplifier 100 is comprised of one or more optical transmitters(Tx1-Txn) 102. Each optical transmitter 102 receives an input signal(freq1-freqn), modulates each respective signal, and transmits atransmitter output optical signal to a multiplexer 104. In one aspect,the transmitters 102 can be, for example, FTTH transmitters with SBSsuppression technology as available from Scientific-Atlanta, Inc., aCisco Company, of Lawrenceville, Ga., though other transmitters arecontemplated within the scope of this invention.

The input signals (freq1-freqn) can be comprised of broadcastinformation, directed information, narrowcast information, or anycombination of broadcast, directed, and narrowcast information.Referring to FIGS. 1A-1C, it can be seen that there are various andnumerous combinations of inputs to the transamplifier. For instance, asshown in the embodiment of FIG. 1B, the input signals to thetransamplifier are comprised of n narrowcast signals (NCast1-NCastn) andone broadcast signal (BCast) that is connected with each of thenarrowcast signals. Similarly, in FIG. 1C, each input signal iscomprised of a discrete narrow cast signal (NCast1-NCastn) incombination with a broadcast signal (BCast). It is to be appreciatedthat these are just a few input signal arrangements, and that numerousothers are contemplated under the scope of the invention.

The output of each optical transmitter 102 is operatively connected withan input of the multiplexer 104, as are known in the art to one ofordinary skill. The transmitter output optical signal of each opticaltransmitter 102, which is provided to the multiplexer 104, has arespective transmitted power level. For example, in an instance wherefour transmitter output signals are provided to the multiplexer 104, thetransmitted power levels of the respective transmitter output signalscan each be 10 dBm.

The multiplexer 104 is an optical multiplexer, as are known in the art,and has a plurality of inputs and at least one output. The outputs ofeach of the one or more optical transmitters 102 are operativelyconnected with a respective one of the plurality of inputs of themultiplexer 104. The output of the multiplexer 104 is configured totransmit a combined optical signal comprised of the transmitter outputoptical signals having respective transmitted power levels. The combinedoptical signal has a combined power level.

The combined optical signal, having a combined power level, is providedto the input of an optical amplifier 106. The optical amplifier can be asingle-doped, fiber-doped amplifier such as an EDFA, a multiple-doped,fiber-doped amplifier such as a cladding pumped amplifier, or a solidstate amplifier. The optical amplifier 106 has an output, and furthercharacterized as having a Relative Intensity Noise (RIN) level. ThoughRIN is a characteristic of an optical amplifier, it is also inherent inthe transmitter laser and laser to modulator interaction, thus resultingin RIN produced by the transamplifier. Further RIN can be produced bythe system or network to which the transamplifier is connected, and suchRIN can be caused by intermodulation noise from transmitter, fiber, andfiber scattering; diode and electronic characteristics in the opticalreceiver module; and fiber non-linear interaction between multiplewavelengths. RIN degrades the RF signal to noise (CNR) parameter perchannel over the whole operating band, the intermodulation noise createsharmonic beating effects (CSO from second orders, CTB from third orders)spread statistically throughout the operating band, and scatteringphenomena appear due to the high launch powers necessary for costeffective delivery of signal. All of these if unchecked reduce thenecessary quality of service. A characteristic of an optical amplifieris that the power level of an input signal to the amplifier affects theamount of RIN produced by the optical amplifier. For instance, if thepower level of the input signal is above a threshold level (P_(min)), insome instances the RIN produced by the optical amplifier is severelyreduced or negligible. Further, for a cladding pumped amplifier, P_(min)is required to be at a minimum level for proper operation of thecladding pumped amplifier. Typical P_(min) levels for a cladding pumpedamplifier can be about 15 dBm and about 5 dBm for an EDFA amplifier.

The input of the optical amplifier 106 is operatively connected with theoutput of the optical multiplexer 104. The optical amplifier 106receives the combined optical signal from the multiplexer 104, amplifiesit, and transmits the amplified combined optical signal to its output.In one aspect, the optical amplifier can be a multiple-doped,fiber-doped amplifier such as a cladding pumped amplifier. One suchcladding pumped amplifier is erbium (Er)-ytterbium (Yb) amplifierdescribed in U.S. Pat. No. 5,225,925 issued to Grubb et al. on Jul. 6,1993 and hereby incorporated by reference in its entirety, though othercladding pumped amplifiers are contemplated within the scope of thisinvention. In another aspect, the optical amplifier can be single-doped,doped-fiber amplifier such as an Erbium Doped Fiber Amplifier (EDFA), asare known in the art to one of ordinary skill. The EDFA can boost anoptical signal. By way of example, an EDFA can comprise several metersof glass fiber doped with erbium ions. When the erbium ions are excitedto a high energy state, the doped fiber changes from a passive medium toan active amplifying medium. In other aspects, the optical amplifier canbe a solid-state amplifier or other amplifiers configured to amplify anoptical signal.

Further comprising the transamplifier 100 is an optical demultiplexer108, as are known in the art, and having an input and a plurality ofoutputs. In one instance, the input of the demultiplexer 108 isoperatively connected to the output of the optical amplifier 106. Theoptical demultiplexer 108 is configured to receive the amplifiedcombined optical signal from the optical amplifier 106, split theamplified combined optical signal into a plurality of discrete outputoptical signals of varying power and wavelength selections, and transmiteach discrete output optical signal to one or more of the plurality ofoutputs of the demultiplexer 108. The wavelength selections can becomprised of a signal having a single wavelength, or a signal comprisedof a plurality of wavelengths. The signal can be further spilt using,for example, a 1×N splitter, as are known in the art. In another aspect,and as shown in FIG. 1D, the output of the optical amplifier 106 can beprovided to an optical splitter 110, and then provided to one or moreoptical demultiplexer 108.

In operation, the combining of the transmitter output optical signalsresults in a combined optical signal having a combined power level. Ifthis combined power level is greater than the threshold power level(P_(min)), then, if the optical amplifier is a cladding pumpedamplifier, the amplifier is operational. This results in atransamplifier having an acceptable quality of a communications channelfor each of the discrete output optical signals. The transamplifierfurther allows a system operator to not only broadcast but alsonarrowcast to each individual group according to its differentiatedneeds. In one aspect, acceptable quality of a communications channel foreach of the discrete output optical signals is determined by a signal tonoise ratio (SNR). In another aspect, the acceptable quality of acommunications channel for each of the discrete output optical signalsis determined by a carrier to noise ratio (CNR). CNR from theperspective of a receiver operatively connected to the network comprisedof a transamplifier, can be determined by the equation

${{C\; N\; R} = {\left( \frac{1}{2 \cdot B} \right)\frac{m^{2} \cdot I^{2}}{{2\;{e \cdot I}} + n^{2} + {R\; I\;{N \cdot I^{2}}}}}},$where m is optical modulation per channel, I is an average receivedphotocurrent, B is noise bandwidth per channel, n is thermal noiseintroduced by an optical receiver referred to the photocurrent, e iselectron charge and RIN is the relative intensity noise of the system,including all parts of the transamplifier and its link interaction.

FIG. 2 is an illustration of a system for transporting video, voice anddata over a fiber optic network in an embodiment according to thepresent invention. In FIG. 2, the system is comprised of one or moreoptical line terminations (OLTs) 202 operatively coupled to afiber-optic network. An OLT 202 is responsible for transmitting voiceand data downstream to one or more ONUs 204, and allocating upstreambandwidth to the ONUs 204. Each ONU 204 is operatively coupled to thefiber-optic network. Further comprising the system is a transamplifier100, as previously described herein. Information signals, such as, forexample, video, whether broadcast, narrowcast, directed, combinationsthereof, or otherwise are provided to the fiber optic network from thetransamplifier 100 through one or more wavelength-division multiplexers(WDMs) 206.

The WDM 206 allows for the transmission of two or more signals bysending the signals at different wavelengths through the same fiber. Thesystem can further comprise a splitter 208 to service a furtherplurality of end users. Each fiber leaving the splitter 208 can becoupled to an optical network unit, such as ONU 204. In one aspect, thefiber optic network is a passive optical network (PON), which are knownin the art and further described herein.

IV. EXAMPLE METHODS

In one embodiment, illustrated in FIG. 3, methods are provided fortuning a transamplifier according to the present invention. The methodcomprises the steps of determining the desired characteristics for eachof a plurality of output discrete optical signals from a transamplifier302; providing a plurality of input signals to the inputs of thetransamplifier 304; and analyzing each of the plurality of outputdiscrete optical signals from the transamplifier respective to thedesired characteristics for the output signals 306. At step 308, it isdetermined whether the desired characteristics (as determined in step302) have been met, or substantially met. If not, then the process goesto step 310, where the transamplifier is adjusted to obtain the desiredcharacteristics for the output signals. If, however, at step 308 it isdetermined that the desired characteristics (as determined in step 302)have been met, or substantially met, then the process goes to step 312,where it ends.

Determining the desired characteristics for each of a plurality ofoutput discrete optical signals from a transamplifier 302 includesdetermining the desired power level for one or more of the plurality ofoutput discrete optical signals; the wavelengths for one or more of theplurality of output discrete optical signals; the CNR for one or more ofthe plurality of output discrete optical signals; and carrier distortionratios (e.g., composite second order (CSO) and composite triple beat(CTB)) for one or more of the plurality of output discrete opticalsignals, bit error rate (BER) and the like.

Adjusting the transamplifier to obtain the desired characteristics forthe output signals (step 310) includes adjusting one or more of anamplitude of one or more of the plurality of input signals to thetransamplifier; adjusting the wavelength of one or more of the pluralityof input signals; adjusting input power associated with one or more ofthe plurality of input signals; adjusting output power of one or more ofthe optical transmitters; adjusting power input to the opticalamplifier; adjusting the wavelength of an amplification signal providedby the optical amplifier; adjusting the electronic pre-distortion of oneor more of the plurality of input signals to the transamplifier; byselection or replacement of the components of the transamplifierincluding a laser having certain characteristics for the opticalamplifier.

While the methods and systems have been described in connection withpreferred embodiments and specific examples, it is not intended that thescope be limited to the particular embodiments set forth, as theembodiments herein are intended in all respects to be illustrativerather than restrictive.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatan order be inferred, in any respect. This holds for any possiblenon-express basis for interpretation, including: matters of logic withrespect to arrangement of steps or operational flow; plain meaningderived from grammatical organization or punctuation; the number or typeof embodiments described in the specification.

It will be apparent to those skilled in the art that variousmodifications and variations can be made without departing from thescope or spirit. Other embodiments will be apparent to those skilled inthe art from consideration of the specification and practice disclosedherein. It is intended that the specification and examples be consideredas examples only, with a true scope and spirit being indicated by thefollowing claims.

1. A method of tuning a transamplifier comprising: providing a pluralityof analog input signals to a transamplifier, the transamplifiercomprised of: one or more optical transmitters, wherein each opticaltransmitter receives one of the analog input signals and transmits atransmitter analog output optical signal having a respective transmittedpower level; an optical multiplexer having a plurality of inputs and atleast one output, wherein each of the one or more optical transmittersare operatively connected with a respective one of the plurality ofinputs and the output is configured to transmit a combined analogoptical signal comprised of each of the transmitter analog outputoptical signals having respective transmitted power levels and thecombined analog optical signal having a combined power level; acladding-pumped optical amplifier having an input and an output, whereinthe input receives the combined analog optical signal, amplifies it andtransmits an amplified combined analog optical signal to the output ofthe cladding-pumped optical amplifier; and an optical demultiplexerhaving an input and a plurality of outputs, wherein the input isconfigured to receive at least a portion of the amplified combinedanalog optical signal, split the amplified combined analog opticalsignal into a plurality of discrete analog output optical signals ofvarying power and wavelength selections, and transmit each discreteanalog output optical signal to one of the plurality of outputs;determining desired characteristics for each of the plurality of outputdiscrete analog optical signals; analyzing each of the plurality ofoutput discrete analog optical signals; and adjusting the transamplifierto obtain the desired characteristics for each of the plurality ofoutput discrete analog optical signals.
 2. The method of claim 1,wherein adjusting the transamplifier to obtain the desiredcharacteristics for each of the plurality of output discrete analogoptical signals comprises adjusting one or more of an amplitude of oneor more of the plurality of analog input signals, the wavelength of oneor more of the plurality of analog input signals, input power associatedwith one or more of the plurality of analog input signals, output powerof one or more of the optical transmitters, power input to thecladding-pumped optical amplifier, wavelength of an amplification signalprovided by the cladding-pumped optical amplifier, electronicpre-distortion compensation of one or more of the plurality of analoginput signals to the transamplifier, electronic pre-distortioncompensation of one or more electrical signals within thetransamplifier, optical pre-distortion compensation of one or moreanalog optical signals within the transamplifier, and by selection of alaser having certain characteristics for the cladding-pumped opticalamplifier.
 3. The method of claim 1, wherein determining desiredcharacteristics for each of the plurality of output discrete analogoptical signals comprises determining desired characteristics forcarrier to noise ratio (CNR) and one or more carrier to distortionratios.
 4. The method of claim 1, wherein the combined power level ofthe combined analog optical signal is greater than of approximately 15dBm at the input of the cladding-pumped optical amplifier such that RINcharacteristics associated with the cladding-pumped optical amplifierare substantially mitigated.
 5. The method of claim 1, wherein thetransamplifier further comprises an optical splitter having one inputand N outputs, wherein the optical splitter receives the amplifiedcombined analog optical signal from the cladding-pumped opticalamplifier and splits it into N analog signals such that the opticaldemultiplexer receives the portion of the amplified combined analogoptical signal from the optical splitter.
 6. The method of claim 1,wherein a quality of a communications channel for each of the discreteanalog output optical signals of the transamplifier is determined by asignal to noise ratio (SNR).
 7. The method of claim 1, wherein a qualityof a communications channel for each of the discrete analog outputoptical signals of the transamplifier is determined by a carrier tonoise ratio (CNR).
 8. The method of claim 1, wherein each analog inputsignal is a video signal.
 9. The method of claim 1, wherein each analoginput signal is broadcast information, narrowband information, orcombined broadcast and narrowband information.
 10. A system fortransporting voice, data and video signals over a fiber optic network,comprising: an optical line termination (OLT) operatively coupled to thefiber-optic network; an optical network unit (ONU) operatively coupledto the fiber-optic network; and a transamplifier operatively coupled tothe fiber-optic network, wherein the transamplifier is comprised of: oneor more optical transmitters, wherein each optical transmitter receivesan analog input signal and transmits a transmitter output analog opticalsignal having a respective transmitted power level; an opticalmultiplexer having a plurality of inputs and at least one output,wherein each of the one or more optical transmitters are operativelyconnected with a respective one of the plurality of inputs and theoutput is configured to transmit a combined analog optical signalcomprised of each of the transmitter output analog optical signalshaving respective transmitted power levels and the combined analogoptical signal having a combined power level; an optical amplifierhaving an input and an output, wherein the input receives the combinedanalog optical signal, amplifies it and transmits an amplified combinedanalog optical signal to the output of the optical amplifier, thecombined power level of the combined analog optical signal being greaterthan a threshold power level (P_(min)) at the input of the opticalamplifier such that RIN characteristics associated with the opticalamplifier are substantially mitigated; and an optical demultiplexerhaving an input and a plurality of outputs, wherein the input isconfigured to receive at least a portion of the amplified combinedanalog optical signal, split the amplified combined analog opticalsignal into a plurality of discrete analog output optical signals ofvarying power and wavelength selections, and transmit each discreteanalog output optical signal to one of the plurality of outputs; and oneor more wavelength-division multiplexers (WDMs), wherein the discreteanalog output optical signals of the transamplifier are combined withanalog voice and data signals from the OLT using WDMs and transported tothe ONU through the fiber-optic network.
 11. The system of claim 10,wherein the fiber optic network is a passive optical network (PON). 12.The system of claim 10, wherein each input analog signal is a videosignal.
 13. The system of claim 10, wherein each input analog signal isbroadcast information, narrowband information, or combined broadcast andnarrowband information.
 14. The system of claim 10, wherein the combinedpower level of the combined analog optical signal is greater thanapproximately 15 dBm at the input of the optical amplifier.
 15. Atransamplifier apparatus operative coupled to a fiber-optic network, thetransamplifier comprising: one or more optical transmitters in thetransamplifier apparatus, wherein each optical transmitter receives ananalog input signal and transmits a transmitter analog output opticalsignal having a respective transmitted power level; an opticalmultiplexer in the transamplifier apparatus having a plurality of inputsand at least one output, wherein each of the one or more opticaltransmitters are operatively connected with a respective one of theplurality of inputs and the output is configured to transmit a combinedanalog optical signal comprised of each of the transmitter analog outputoptical signals having respective transmitted power levels and thecombined analog optical signal having a combined power level; an opticalamplifier in the transamplifier apparatus having an input and an output,wherein the input receives the combined analog optical signal, amplifiesit and provides an amplified combined analog optical signal to theoutput of the optical amplifier, the combined power level of thecombined analog optical signal being greater than a threshold powerlevel (P_(min)) at the input of the optical amplifier such that RINcharacteristics associated with the optical amplifier are substantiallymitigated; and an optical demultiplexer in the transamplifier apparatushaving an input and a plurality of outputs, wherein the input isconfigured to receive at least a portion of the amplified combinedanalog optical signal, split the amplified combined analog opticalsignal into a plurality of discrete analog output optical signals ofvarying power and wavelength selections, and transmit each discreteanalog output optical signal to one of the plurality of outputs fortransmission via an optical fiber transmission medium to one or morewavelength-division multiplexers (WDMs), wherein the discrete analogoutput optical signals are combined with analog voice and data signalsfrom an optical line termination (OLT) using the WDMs and transported toan optical network unit (ONU) through the fiber-optic network.
 16. Atransamplifier apparatus comprising: one or more optical transmitters inthe transamplifier apparatus, wherein each optical transmitter receivesone of a respective one or more analog input signals and transmits atransmitter analog output optical signal having a respective transmittedpower level; an optical multiplexer in the transamplifier apparatushaving a plurality of inputs and at least one output, wherein each ofthe one or more optical transmitters are operatively connected with arespective one of the plurality of inputs and the output is configuredto transmit a combined analog optical signal comprised of each of thetransmitter analog output optical signals having respective transmittedpower levels and the combined analog optical signal having a combinedpower level; a cladding-pumped optical amplifier in the transamplifierapparatus having an input and an output, wherein the input receives thecombined analog optical signal, amplifies it and provides an amplifiedcombined analog optical signal to the output of the cladding-pumpedoptical amplifier; and an optical demultiplexer in the transamplifierapparatus having an input and a plurality of outputs, wherein the inputis configured to receive at least a portion of the amplified combinedanalog optical signal, split the amplified combined analog opticalsignal into a plurality of discrete analog output optical signals ofvarying power and wavelength selections, and transmit each discreteanalog output optical signal to one of the plurality of outputs fortransmission via an optical fiber transmission medium; wherein at leastone of the one or more transmitters, the optical multiplexer, thecladding-pumped optical amplifier, and the optical demultiplexer areadjustable to obtain desired characteristics for each of the pluralityof discrete analog output optical signals in response to a determinationof the desired characteristics and an analysis of each of the pluralitydiscrete analog output optical signals.